Electron beam generator including a plasma beam in a condensing chamber



p 1968 B0 BREITHOLTZ ETAL ELECTRON BEAM GENERATOR INCLUDING A PLASMABEAM IN A CONDENSING CHAMBER Filed May 25, 1966 United States Patent3,379,909 ELECTRON BEAM GENERATOR INCLUDING A PLASMA BEAM IN ACONDENSING CHAMBER Bo Breitholtz and Clas Jacobsen, Vasteras, Sweden,as-

signors to Allmiinna Svenska Elektriska Aktiebolaget, Vasteras, Sweden,a Swedish corporation Filed May 25, 1966, Ser. No. 552,791 Claimspriority, application Sweden, May 25, 1965, 6,827/65 7 Claims. (Cl.313-34) ABSTRACT OF THE DISCLOSURE A device for generating an electronbeam includes means for generating a plasma beam in a condensingchamber. At the side of condensing chamber is an electron chamber havingan annular anode and a catch anode. A source of voltage is connectedbetween a plasma emitting cathode and the two anodes. The direction ofthe voltage between said two anodes is substantially perpendicular tothe direction of the plasma beam.

In many different technical fields there is a great demand for devices,which can emit large amounts of electrons, corresponding to currentintensities of hundreds of amperes, without simultaneous emission ofneutral atoms and ions. The only electronic emitters known at present,that is those emitters which do not simultaneously emit neutral atomsand ions, are for example different types of directly heated cathodes,cold cathodes and devices for field emission. From these devices,however, only a limited current of a size of some tens of amperes can beobtained.

The present invention relates to a device by means of which it ispossible to generate a continuous electronic current of a size whichconsiderably exceeds what has been possible previously. Thecharacteristics of the invention are evident from the followingdescription.

A description of a possible embodiment of the invention as it is shownin the enclosed drawing is given in the following.

A cathode vessel 1 contains mercury 2 which constitutes the cathodematerial of the device. The mercury can be heated by means of a heatingcoil 3. The vapor generated by the heating is led through a tube 4 intoa condensing chamber 5 electrically insulated from the cathode vessel inwhich chamber the tube ends with a nozzle 6. In the condensing chamberat least the wall 7 of the condensing chamber opposite the nozzle iscooled, so that the flowing Hg-vapor is condensed and runs back into thecathode vessel through a condensor tube 8. It is also possible to haveall the walls cooled. Due to the large amount of vapor generation in thecathode vessel and resulting high pressure of the Hg-vapor as well asthe low pressure which is kept in the condensing chamber, a vapor beamfrom the nozzle is projected with a very high speed into the condensingchamber. The low pressure is maintained by means of a vacuum pump 12.

In order to ionize the gas which flows from the cathode vessel throughthe tube into the condensing chamber an annular auxiliary anode 9 isinserted in the tube and connected to a voltage source 10 which is alsoconnected to the Hg-cathode. The voltage drop between the auxiliaryanode and the cathode makes the gas in the tube ionize and a plasmastream is obtained which has a high speed when leaving the nozzle 6. Theionization can be increased further by an ionization coil 11 arrangedaround the tube 4 which coil is fed with a high frequency current. Bymeans of these ionization devices a very strong plasma stream in thecondensing chamber 5 is obtained.

An electron chamber 13 is arranged at the end of the 3,379,909 PatentedApr. 23, 1968 condensing chamber where the nozzle ends. The chamber hasa bulge 14 having a wall which is mainly parallel to the direction ofthe plasma stream and in this wall an opening 15 is made. Inside thebulge there is an annular anode 16, which is connected with the cathodeover a voltage source 17. In the extension of the symmetrical axis ofthe annular anode there is a catch or extractor anode 18 which isconnected with the cathode. In this connection a voltage source 19 canbe included, if it is found suitable.

The voltage drop between the annular anode 16 and the cathode causes anelectron stream from the Hg-cathode through the tube 4 and the annularanode 16 to the anode 18. The plasma stream has such a high speed whenpassing the opening 15 that ions and neutral gas atoms continue straightforward, while the electrons due to their negative charge are suckedinto the annular anode by the electric field and a pure electron streamis obtained in the electron chamber 13.

In a variation of the invention the annular anode is not used, andinstead the voltage generating the electron stream is placed between thecatch anode 18 and the cathode. It is of course possible to combinethese two variations.

The electron chamber is provided with a gas inlet 20 and a vacuum pump21. It is thereby possible to insert any suitable gas in the vacuumchamber. The density of this gas must, however, not be so large that thegas which is forced down through the opening 15 in the acceleratingplasma causes too many collisions with cathode material atoms, so thatthese are spread upwards and into the electron chamber. The plasma whichflows to the right also works as a diffusion pump for the gas which isforced down from the electron chamber, whereby a certain amount of gasis obtained at the condensing wall 7. This gas is taken away by means ofthe vacuum pump 12.

In time it is impossible to avoid a certain amount of vapor of cathodematerial being forced into the electron chamber. In order to preventthis vapor from condensing on the inner surfaces, these are kept at sucha high temperature that the vapor pressure of the vapor at thistemperature is higher than the real vapor pressure of the vapor due tothe flux through the opening 15. It can furthermore be necessary tocontinuously pump away so much vapor by means of the vacuum pump 21 thata sufficiently low vapor pressure can be maintained. If another gas isused in the electron chamber, the vacuum pump will pump out this gas andtherefore there is always a certain consumption in such cases.

The necessary gas current for obtaining the plasma stream can also betaken from a tank containing a suitable gas under high pressure. The gasstream is ionized by means of a gas discharge between said auxiliaryanode 9 and an electronic emitter connected thereto across a voltagesource. This emitter is preferably arranged in the vicinity of the gasgenerating device and can consist of a cathode of mercury known per seor other metal, for, example cesium, where the electrons are emittedfrom the cathode spot. It is also possible to use other devices forgeneration of a stream of gas or stream.

The catch anode 18 can also be placed outside the electron chamber 13,so that the whole space of the chamber is available for examinations andexperiments. This is especially suitable if the electron stream is to beused in a gas with a pressure which is too high for use in the electronchamber. For this purpose an opening which does not let gas through isarranged partly between the condensing chamber and the electron chamberand partly between the electron chamber and the catch anode.

We claim:

1. A device for generating a continuous electronic current between ananode and a cathode, Comprising means for generating a gaseous streamwith a high speed, means in the path of such gaseous stream for ionizingsaid stream to a plasma stream, an anode arranged at the side of theplasma stream positioned to extract electrons therefrom, and a cathodeconnected to said anode, the gaseous stream generating means comprisinga cathode vessel containing an electron emitting metal and provided witha heating device, said metal constituting the cathode, a condensingchamber, a tube connecting the cathode vessel to the condensing chamber,the tube ending in the condensing chamber in a nozzle, means for coolingat least the Wall of the condensing chamber opposite the nozzle, and areturn tube for condensed metal leading from the condensing chamber tothe cathode vessel.

2. A device according to claim 1, the tube leading from the cathodevessel to the condensing chamber being provided with ionizing meansincluding an annular auxiliary anode.

3. A device according to claim 1, the tube leading from the cathodevessel to the condensing chamber being provided with ionizing meansincluding a device for high frequency ionization of the gaseous stream.

4. A device according to claim 1, an electron extracting chamberarranged laterally with respect to the plasma stream in the condensingchamber.

5. A device according to claim 4, the anode comprising an annular anodearranged in the electron extracting chamber.

6. A device according to claim 4, having a catch anode arranged insidethe electron extracting chamber and connected to the cathode.

7. A device according to claim 6, a voltage source in the connectionbetween said catch anode and the cathode.

References Cited UNITED STATES PATENTS 2,754,442 7/1956 Boutry 3 132303,275,867 9/1966 Tsuchimoto 313-63 2,943,239 6/1960 Goodman 313-61 XFOREIGN PATENTS 1,093,152 11/1954 France.

OTHER REFERENCES Weinman et a1., Negative Hydrogen Ion Source,"published in The Review of Scientific Instruments, v01. 27, No. 5, May1956, pp. 289-293 relied on. Copy in 313-63.

JAMES W. LAWRENCE, Primary Examiner.

STANLEY D. SCHLOSSER, Examiner.

R. L. JUDD, Assistant Examiner.

